Charge Pump Suitable for Low Input Voltages

ABSTRACT

A charge pump circuit suitable for low input voltages is presented. The charge pump circuit has a first clock signal generator, a second clock signal generator and n voltage doubler circuits. The voltage doubler has an input, an output, a first capacitor connected to the first clock signal generator, a second capacitor connected to the second clock signal generator, a first NMOST having the source connected to the input and the drain connected to the first capacitor, a second NMOST having the connected to the source of the first NMOST and the drain connected to second capacitor, a first PMOST having the drain connected to the first capacitor and the source connected to the output, a second PMOST having the source connected to the source of the first PMOST and the drain connected to the second capacitor.

TECHNICAL FIELD

The invention relates to voltage doubler circuits, and in particular, to charge pumps circuits implemented with voltage doubler circuits.

BACKGROUND

A thermoelectric generator (TEG) converts body heat into electricity to supply power to sensors. However, the output voltage of a TEG is usually very low (often a few hundred millivolt or less). Therefore, a TEG requires a low-voltage high-efficiency voltage converter.

Usually, this is achieved by using an inductive direct current-to-direct current (DC-DC) converter, supported by a start-up circuit. The start-up circuit must be able to start-up by itself and generate a sufficiently high voltage for the control circuits of the inductive DC-DC converter to operate. This start-up circuit is very often a capacitive charge-pump circuit. An alternative method would be to omit the inductive DC-DC converter and to perform all the power transfer by using the capacitive charge-pump circuit, and not only during start-up.

“An experimental 1.5V 64 Mb DRAM” by Y. Nakagome, H. Tanaka, et al., IEEE J. Solid-State Circuits, vol. 26, no. 4, pp. 465-472, April 1991 describes a basic voltage-doubler as used in many charge pump circuits.

FIG. 1 illustrates a known charge pump circuit implemented using voltage doubler circuits. The charge-pump circuit 10 of FIG. 1, seen from down to up, comprises a series circuit of first voltage doubler circuit 1, a second voltage doubler circuit 2, and a third voltage doubler circuit 3.

The charge pump circuit 10 of FIG. 1 comprises a plurality of transistors T_(i) (i=1, 2, . . . , 12). Each one of these transistors T_(i) has a respective gate G_(i), a source S_(i), and a drain D_(i). For the sake of simplicity, a transistor T_(i) will be called an i^(th) transistor in the specification hereinafter. The charge pump circuit 10 of FIG. 1 also comprises a plurality of capacitors C_(j) (j=1, 2, . . . , 6). Each one of these capacitors C_(j) has a first end c_(j1)and a second end c_(j2). It is observed that the reference number concerned may be different in the claims, as they may appear in another order in the claims.

FIG. 1, also shows the voltage received and delivered by each of the voltage doubler circuits: the first voltage doubler circuit 1 is arranged to receive a voltage V_(in1) from the input V_(in) of the charge pump circuit 10 and to deliver a voltage V_(out1) to the second voltage doubler circuit 2, the second voltage doubler circuit 2 is arranged to receive a voltage V_(in2) and to deliver a voltage V_(out2) to the third voltage doubler circuit 3, and the third voltage doubler circuit 3 is arranged to receive a voltage V_(in3) and to deliver a voltage V_(out3) to the output V_(out) of the charge pump circuit 10 of FIG. 1.

The charge pump circuit 10 of FIG. 1 comprises a first clock signal generator CLK_(p) and a second clock signal generator CLK_(n). The first clock signal generator CLK_(p) is configured to generate a first clock signal and the a second clock signal generator CLK_(n) is configured to generate a second clock signal, wherein the second clock signal is low when the first clock signal is high and the second clock signal is high when the first clock signal is low.

The charge pump circuit 10 of FIG. 1 comprises a capacitor C_(out) having a first end c_(out1) and a second end c_(out2). The first end c_(out1) of C_(out) is connected to the output V_(out) of the charge pump circuit 10 of FIG. 1. The second end c_(out2) of C_(out) is connected to the ground.

The first voltage doubler circuit of the charge pump circuit 10 of FIG. 1 includes a first N-type metal oxide semiconductor transistor (NMOST) T₁, a second N-type metal oxide semiconductor transistor T₂, a third P-type metal oxide semiconductor transistor (PMOST) T₃, and a fourth P-type metal oxide semiconductor transistor T₄. The first voltage doubler circuit of the charge pump circuit 10 of FIG. 1 also includes a first capacitor C₁ having a first end c₁₁ and a second end c₁₂ and a second capacitor C₂ having a first end c₂₁ and a second end c₂₂ . The first NMOST T₁ and the second NMOST T₂ have their source terminals S₁ and S₂ connected to the input V_(in) of the charge pump circuit and their drain terminals D₁ and D₂ are connected respectively to the second end c₁₂ of capacitor C₁ and to the first end c₂₁ of capacitor C₂. The drain terminal D₁ of the first NMOST T₁ is also connected to the drain terminal D₃ of the third PMOST T₃, to the gate terminal G₄ of fourth PMOST T₄ and to the gate terminal G₂ of second NMOST T₂. The drain terminal D₂ of the second NMOST T₂ is also connected to the drain terminal D₄ of the fourth PMOST T₄, to the gate terminal G₃ of third PMOST T₃ and to the gate terminal G₁ of first NMOST T₁, The third PMOST T₃ and the fourth PMOST T₄ have their source terminals S₃ and S₄ connected to the output of the first double voltage circuit.

The output V_(out1) of the first double voltage circuit 1 of the charge pump circuit 10 of FIG. 1 is connected to the input of the second voltage doubler circuit of the charge pump circuit.

The second voltage doubler circuit of the charge pump circuit 10 of FIG. 1 includes a fifth NMOST T₅, a sixth NMOST T₆, a seventh PMOST T₇, and an eighth PMOST T₈. The second voltage doubler circuit of the charge pump circuit 10 of FIG. 1 also includes a third capacitor C₃ having a first end c₃₁ and a second end c₃₂ and a fourth capacitor C₄ having a first end c₄₁ and a second end c₄₂. The fifth NMOST T₅ and the sixth NMOST T₆ have their source terminals S₅ and S₆ connected to the input V_(in2) of the second voltage doubler circuit 2 of the charge pump circuit 10 of FIG. 1, and their drain terminals D₅ and D₆ connected respectively to the second end c₃₂ of capacitor C₃ and to the first end c₄₁ of capacitor C₄. The drain terminal D₅ of the fifth NMOST T₅ is also connected to the drain terminal D₇ of the seventh PMOST T₇, to the gate terminal G₈ of eighth PMOST T₈ and to the gate terminal G₆ of sixth NMOST T₆. The drain terminal D₆ of the sixth NMOST T₆ is also connected to the drain terminal D₈ of the eighth PMOST T₈, to the gate terminal G₇ of seventh PMOST T₇ and to the gate terminal G₅ of fifth NMOST T₅. The seventh PMOST T₇ and the eighth PMOST T₈ have their source terminals S₇ and S₈ connected to the output V_(out2) of the second double voltage circuit 2.

The output V_(out2) of the second double voltage circuit 2 of the charge pump circuit 10 of FIG. 1 is connected to the input V_(in3) of the third voltage doubler circuit 3 of the charge pump circuit 10.

The third voltage doubler circuit 3 of the charge pump circuit 10 of FIG. 1 includes a ninth NMOST T₉, a tenth NMOST T₁₀, a eleventh PMOST T₁₁, and a twelfth PMOST T₁₂. The third voltage doubler circuit of the charge pump circuit 10 of FIG. 1 also includes a fifth capacitor C₅ having a first end c₅₁ and a second end c₅₂ and a sixth capacitor C₆ having a first end c₆₁ and a second end c₆₂. The ninth NMOST T₉ and the tenth NMOST T₁₀ have their source terminals S₉ and S₁₀ connected to the input of the third voltage doubler circuit of the charge pump circuit 10 of FIG. 1, and their drain terminals D₉ and D₁₀ connected respectively to the second end c₅₂ of capacitor C₅ and to the first end c₆₁ of capacitor C₆. The drain terminal D₉ of the ninth NMOST T₉ is also connected to the drain terminal D₁₁ of the eleventh PMOST T₁₁, to the gate terminal G₁₂ of twelfth PMOST T₁₂ and to the gate terminal G₁₀ of tenth NMOST T₁₀. The drain terminal D₁₀ of the tenth NMOST T₁₀ is also connected to the drain terminal D₁₂ of the twelfth PMOST T₁₂, to the gate terminal G₁₁ of eleventh PMOST T₁₁ and to the gate terminal G₉ of ninth NMOST T₉ The eleventh PMOST T₁₁ and the twelfth PMOST T₁₂ have their source terminals S₁₁ and S₁₂ connected to the output V_(out3) of the third double voltage circuit 3.

The output V_(out3) of the third double voltage circuit 3 of the charge pump circuit 10 of FIG. 1 is connected to the output V_(out) of the charge pump circuit 10.

The first clock signal generator CLK_(p) of the charge pump circuit 10 of FIG. 1 is connected to the first end c₁₁ of capacitor C₁, to the first end c₃₁ of capacitor C₃, and to the first end c₅₁ of capacitor C₅. The second clock signal generator CLK_(n) of the charge pump circuit 10 of FIG. 1 is connected to the second end c₂₂ of capacitor C₂, to the second end c₄₂ of capacitor C₄, and to the second end c₆₂ of capacitor C₆.

Now it will be explained how the charge pump circuit 10 of FIG. 1 works.

The first clock signal generator CLK_(p) of the charge pump circuit 10 of FIG. 1 oscillates between a low value of zero and a high value of V_(DD). The second clock signal generator CLK_(n) of the charge pump circuit 10 of FIG. 1 oscillates between a high value of V_(DD) and a low value of zero.

In phase 1, the first clock signal generator CLK_(p) is low, the second clock signal CLK_(n) is high, the first NMOST T₁ and the fourth transistor PMOST T₄ are conducting while the second NMOST T₂ and the third transistor PMOST T₃ are in cut-off. The capacitor C₁ is charging to the input voltage V_(in1). In phase 2, the first clock signal generator CLK_(p) is high, the second clock signal CLK_(n) is low, the first NMOST T₁ and the fourth transistor PMOST T₄ are in cut-off while the second NMOST T₂ and the third transistor PMOST T₃ are conducting, therefore the charge V_(in1) of the capacitor C₁ is transferred partially to the output V_(out1) to keep the output voltage higher than the input voltage V_(in1). The capacitor C₂ does the same but in opposite phases, i.e., in phase 1 its charge is transferred partially to the output V_(out1) and in phase 2 the capacitor C₂ is charging to the input voltage V_(in1). By cascading several voltage doubling stages, an output voltage V_(out) higher than the input voltage V_(in) can be obtained, as each double voltage circuit provides a higher input voltage to the following double voltage circuit.

In the basic voltage-doubler implemented in FIG. 1, the transistors are turned-on with an absolute gate-source voltage V_(GS) of not more than V_(in)=V_(DD) (assuming that the clock signals are both toggling between 0V and V_(DD), and assuming that the output is equal to twice V_(in), which is the intended operation).

This limited voltage to turn-on the transistors has a negative effect on the drive capability of the circuit and the minimum input voltage V_(in) at which the circuit can operate.

SUMMARY

There is a need to provide an improved charge pump circuit. In a first aspect, the invention provides a charge pump circuit comprising a number n of voltage doubler circuits, with n>1, a first clock signal generator configured to generate a first clock signal, a second clock signal generator configured to generate a second clock signal, wherein the second clock signal is low when the first clock signal is high and the second clock signal is high when the first clock signal is low, wherein each one of the n voltage doubler circuits comprises an input, an output, a first capacitor having a first and a second terminal, wherein the first terminal is connected to the first clock signal generator, a second capacitor having a first and a second terminal, wherein the first terminal is connected to the second clock signal generator, a first N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the first NMOST is connected to the input of the voltage doubler circuit and the drain of the first NMOST is connected to the second terminal of the first capacitor, a second N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the second NMOST is connected to the source of the first NMOST and the drain of the second NMOST is connected to the second terminal of the second capacitor, a first P-type metal oxide semiconductor transistor (PMOST) having a source, a drain and a gate, wherein the drain of the first PMOST is connected to the second terminal of the first capacitor and the source of the first PMOST is connected to the output of the voltage doubler circuit, a second P-type metal oxide semiconductor transistor (PMOST) having a source, a drain and a gate, wherein the source of the second PMOST is connected to the source of the first PMOST and the drain of the second PMOST is connected to the second terminal of the second capacitor, wherein the output of the i-th voltage doubler circuit is the input of the (i+1)-th voltage doubler circuit for every i from 1 to n−1, wherein at least a k-th voltage doubler circuit of the n voltage doubler circuits has the gate of the first PMOST and/or the gate of the second PMOST connected respectively to the second terminal of the second capacitor and/or to the second terminal of the first capacitor of an m-th voltage doubler circuit, wherein m<k, and/or the gate of the first NMOST and/or the gate of the second NMOST connected respectively to the second terminal of the second capacitor and/or to the second terminal of the first capacitor of a j-th voltage doubler circuit, wherein j>k.

By doing so, the gates of the NMOST switches of a voltage doubler circuit and/or the gates of the PMOS switches of a voltage doubler circuit are driven by a higher voltage doubler circuit and/or by a lower voltage doubler circuit. In this way, a higher V_(GS) can be obtained for switching on the transistors.

Compared to a conventional charge-pump (a cascade of conventional voltage doublers), the on-resistance of the switches is significantly reduced for a given input voltage and transistor size. So either the circuit can be smaller for a similar performance, or it can operate at a lower input voltage or it can deliver a larger load current for a similar size.

The dependent claims are focusing on advantageous embodiments.

The person skilled in the art will understand that the features described above may be combined in any way deemed useful.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, aspects of the invention will be elucidated by means of examples, with reference to the drawings. The drawings are diagrammatic and may not be drawn to scale.

The features and effects of the present invention will be explained in more detail below with reference to drawings in which preferred and illustrative embodiments of the invention are shown. The person skilled in the art will realize that other alternatives and equivalent embodiments of the invention can be conceived and reduced to practice without departing from the scope of the present invention.

FIG. 1 illustrates a prior art charge pump circuit with voltage doubler circuits.

FIG. 2 illustrates a charge pump circuit according to one embodiment of the invention.

FIG. 3 illustrates the pump charge circuit of FIG. 2 including start up transistors.

FIG. 4 shows an alternative double voltage circuit.

FIG. 5 illustrates a charge pump circuit according to another embodiment of the invention.

FIG. 6 illustrates the pump charge circuit of FIG. 5 including start up transistors.

FIG. 7 shows simulation results comparing the charge pump circuit of FIG. 1 and the charge pump circuit of FIG. 2.

DESCRIPTION

The examples and embodiments described herein serve to illustrate rather than to limit the invention. The person skilled in the art will be able to design alternative embodiments without departing from the scope of the claims. Reference signs placed in parentheses in the claims shall not be interpreted to limit the scope of the claims. Items described as separate entities in the claims or the description may be implemented as a single or multiple hardware items combining the features of the items described.

FIG. 2 illustrates a charge-pump circuit implemented with voltage doubler circuits. The charge-pump circuit 20 of FIG. 2, seen from down to up, comprises a series circuit of first voltage doubler circuit 21, a second voltage doubler circuit 22, and a third voltage doubler circuit 23. The charge-pump circuit 20 of FIG. 2 may comprise any number of first voltage doubler circuits.

The charge pump circuit 20 of FIG. 2 comprises a plurality of transistors T_(i) (i=1, 2 . . . 14). Each one of these transistors T_(i) has a respective gate G_(i), a source S_(i), and a drain D_(i). For the sake of simplicity, a transistor T_(i) will be called an i^(th) transistor in the specification hereinafter. The charge pump circuit 20 of FIG. 2 also comprises a plurality of capacitors C_(j) (j=1, 2 . . . 8). Each one of these capacitors C, has a first end c_(j1) and a second end c_(j2). It is observed that the reference number concerned may be different in the claims, as they may appear in another order in the claims.

FIG. 2, also shows the voltage received and delivered by each of the voltage doubler circuits: the first voltage doubler circuit 21 is arranged to receive a voltage V_(in1) from the input V_(in) of the charge pump circuit and to deliver a voltage V_(out1) to the second voltage doubler circuit 22, the second voltage doubler circuit 22 is arranged to receive a voltage V_(in2) and to deliver a voltage V_(out2) to the third voltage doubler circuit 23, and the third voltage doubler circuit 23 is arranged to receive a voltage V_(in3) and to deliver a voltage V_(out3) to the output V_(out) of the charge pump circuit 20 of FIG. 2.

The charge pump circuit 20 of FIG. 2 comprises a first clock signal generator CLK_(p1) and a second clock signal generator CLK_(n1). The first clock signal generator CLK_(p1) is configured to generate a first clock signal and the a second clock signal generator CLK_(n1) is configured to generate a second clock signal, wherein the second clock signal is low when the first clock signal is high and the second clock signal is high when the first clock signal is low.

The charge pump circuit 20 of FIG. 2 may comprise a capacitor C_(out) having a first end c_(out1) and a second end c_(out2). The first end c_(out1) of C_(out) may be connected to the output V_(out) of the charge pump circuit 20 of FIG. 2. The second end c_(out2) of C_(out) may be connected to the ground.

The first voltage doubler circuit 21 of the charge pump circuit 20 of FIG. 2 includes a first N-type metal oxide semiconductor transistor (NMOST) T₁, a second N-type metal oxide semiconductor transistor T₂, a third P-type metal oxide semiconductor transistor (PMOST) T₃, and a fourth P-type metal oxide semiconductor transistor T₄. The first voltage doubler circuit 21 of the charge pump circuit 20 of FIG. 2 also includes a first capacitor C₁ having a first end c₁₁ and a second end c₁₂ and a second capacitor C₂ having a first end c₂₁ and a second end c₂₂. The first NMOST T₁ and the second NMOST T₂ have their source terminals S₁ and S₂ connected to the input V_(in) of the charge pump circuit 20 of FIG. 2 and their drain terminals D₁ and D₂ connected respectively to the second end c₁₂ of capacitor C₁ and to the first end c₂₁ of capacitor C₂. The drain terminal D₁ of the first NMOST T₁ is also connected to the drain terminal D₃ of the third PMOST T₃. The drain terminal D₂ of the second NMOST T₂ is also connected to the drain terminal D₄ of the fourth PMOST T₄. The third PMOST T₃ and the fourth PMOST T₄ have their source terminals S₃ and S₄ connected to the voltage output V_(out1) of the first double voltage circuit 21.

The voltage output V_(out1) of the first double voltage circuit 21 of the charge pump circuit 20 of FIG. 2 is connected to the voltage input V_(in2) of the second voltage doubler circuit 22 of the charge pump circuit 20.

The second voltage doubler circuit 22 of the charge pump circuit 20 of FIG. 2 includes a fifth NMOST T₅, a sixth NMOST T₆, a seventh PMOST T₇, and an eighth PMOST T₈. The second voltage doubler circuit 22 of the charge pump circuit 20 of FIG. 2 also includes a third capacitor C₃ having a first end c₃₁ and a second end c₃₂ and a fourth capacitor C₄ having a first end c₄₁ and a second end c₄₂. The fifth NMOST T₅ and the sixth NMOST T₆ have their source terminals S₅ and S₆ connected to the input V_(in2) of the second voltage doubler circuit 22 of the charge pump circuit 20 of FIG. 2, and their drain terminals D₅ and D₆ connected respectively to the second end c₃₂ of capacitor C₃ and to the first end c₄₁ of capacitor C₄. The drain terminal D₅ of the fifth NMOST T₅ is also connected to the drain terminal D₇ of the seventh PMOST T₇ The drain terminal D₆ of the sixth NMOST T₆ is also connected to the drain terminal D₈ of the eighth PMOST T₈. The seventh PMOST T₇ and the eighth PMOST T₈ have their source terminals S₇ and S₈ connected to the output V_(out2) of the second double voltage circuit 22.

The output V_(out2) of the second double voltage circuit 22 of the charge pump circuit 20 of FIG. 2 is connected to the input V_(in3) of the third voltage doubler circuit 23 of the charge pump circuit 20.

The third voltage doubler circuit 23 of the charge pump circuit 20 of FIG. 2 includes a ninth NMOST T₉, a tenth NMOST T₁₀, a eleventh PMOST T₁₁, and a twelfth PMOST T₁₂. The third voltage doubler circuit 23 of the charge pump circuit 20 of FIG. 2 also includes a fifth capacitor C₅ having a first end c₅₁ and a second end c₅₂ and a sixth capacitor C₆ having a first end c₆₁ and a second end c₆₂. The ninth NMOST T₉ and the tenth NMOST T₁₀ have their source terminals S₉ and S₁₀ connected to the input V_(in3) of the third voltage doubler circuit 23 of the charge pump circuit 20 of FIG. 2, and their drain terminals D₉ and D₁₀ connected respectively to the second end c₅₂ of capacitor C₅ and to the first end c₆₁ of capacitor C₆. The drain terminal D₉ of the ninth NMOST T₉ is also connected to the drain terminal D₁₁ of the eleventh PMOST T₁₁. The drain terminal D₁₀ of the tenth NMOST T₁₀ is also connected to the drain terminal D₁₂ of the twelfth PMOST T₁₂. The eleventh PMOST T₁₁ and the twelfth PMOST T₁₂ have their source terminals S₁₁ and S₁₂ connected to the output V_(out3) of the third double voltage circuit 23.

The output V_(out3) of the third double voltage circuit 23 of the charge pump circuit 20 of FIG. 2 is connected to the output V_(out) of the charge pump circuit 20.

The charge pump circuit 20 of FIG. 2 includes a thirteenth NMOST T₁₃, a fourteenth NMOST T₁₄, a seventh capacitor C₇ having a first end c₇₁ and a second end c₇₂, and a eighth capacitor C₈ having a first end c₈₁ and a second end c₈₂.

The source terminal S₁₃ of the thirteenth NMOST T₁₃ and the source terminal S₁₄ of the fourteenth NMOST T₁₄ are connected to the output of the third double voltage circuit 23 of the charge pump circuit 20 of FIG. 2.

The drain terminal D₁₃ of the thirteenth NMOST T₁₃ and the drain terminal D₁₄ of the fourteenth NMOST T₁₄ connected respectively to the second end c₇₂ of capacitor C₇ and to the first end c₈₁ of capacitor C₈. The drain terminal D₁₃ of the thirteenth NMOST T₁₃ is also connected to the gate terminal G₁₄ of the fourteenth NMOST T₁₄. The drain terminal D₁₄ of the fourteenth NMOST T₁₄ is also connected to the gate terminal G₁₃ of the thirteenth NMOST T₁₃.

The first clock signal generator CLK_(p1) of the charge pump circuit 20 of FIG. 2 is connected to the first end c₁₁ of capacitor C₁, to the first end c₃₁ of capacitor C₃, to the first end c₅₁ of capacitor C₅, and to the first end c₇₁ of capacitor C₇. The second clock signal generator CLK_(n1) of the charge pump circuit 20 of FIG. 2 is connected to the second end c₂₂ of capacitor C₂, to the second end c₄₂ of capacitor C₄, and to the second end c₆₂ of capacitor C₆, and to the second end c₈₂ of capacitor C₈.

The first NMOST T₁ of the first double voltage circuit 21 of the charge pump circuit 20 of FIG. 2 has its gate terminal G₁ connected to the first end c₄₁ of capacitor C₄ of the second double voltage circuit 22 of the charge pump circuit 20 of FIG. 2.

The second NMOST T₂ of the first double voltage circuit 21 of the charge pump circuit 20 of FIG. 2 has its gate terminal G₂ connected to the second end c₃₂ of capacitor C₃ of the second double voltage circuit 22 of the charge pump circuit 20 of FIG. 2.

The third PMOST T₃ of the first double voltage circuit 21 of the charge pump circuit 20 of FIG. 2 has its gate terminal G₃ connected to the second clock signal generator CLK_(n1) of the charge pump circuit 20 of FIG. 2.

The fourth PMOST T₄ of the first double voltage circuit 21 of the charge pump circuit 20 of FIG. 2 has its gate terminal G₄ connected to the first clock signal generator CLK_(p1) of the charge pump circuit 20 of FIG. 2.

The fifth NMOST T₅ of the second double voltage circuit 22 of the charge pump circuit 20 of FIG. 2 has its gate terminal G₅ connected to the first end c₆₁ of capacitor C₆ of the third double voltage circuit 23 of the charge pump circuit 20 of FIG. 2.

The sixth NMOST T₆ of the second double voltage circuit 22 of the charge pump circuit 20 of FIG. 2 has its gate terminal G₆ connected to the second end c₅₂ of capacitor C₅ of the third double voltage circuit 23 of the charge pump circuit 20 of FIG. 2.

The seventh PMOST T₇ of the second double voltage circuit 22 of the charge pump circuit 20 of FIG. 2 has its gate terminal G₇ connected to the first end c₂₁ of capacitor C₂ of the first double voltage circuit 21 of the charge pump circuit 20 of FIG. 2.

The eighth PMOST T₈ of the second double voltage circuit 22 of the charge pump circuit 20 of FIG. 2 has its gate terminal G₈ connected to the second end c₁₂ of capacitor C₁ of the first double voltage circuit 21 the charge pump circuit 20 of FIG. 2.

The ninth NMOST T₉ of the third double voltage circuit 23 of the charge pump circuit 20 of FIG. 2 has its gate terminal G₉ connected to the first end c₈₁ of capacitor C₈ of the charge pump circuit 20 of FIG. 2.

The tenth NMOST T₁₀ of the third double voltage circuit 23 of the charge pump circuit 20 of FIG. 2 has its gate terminal G₁₀ connected to the second end c₇₂ of capacitor C₇ of the charge pump circuit 20 of FIG. 2.

The eleventh PMOST T₁₁ of the third double voltage circuit 23 of the charge pump circuit 20 of FIG. 2 has its gate terminal G₁₁ connected to the first end c₄₁ of capacitor C₄ of the second double voltage circuit 22 of the charge pump circuit 20 of FIG. 2.

The twelfth PMOST T₁₂ of the third double voltage circuit 23 of the charge pump circuit 20 of FIG. 2 has its gate terminal G₁₂ connected to the second end c₃₂ of capacitor C₃ of the second double voltage circuit 22 of the charge pump circuit 20 of FIG. 2.

The main difference of the charge pump circuit 20 of FIG. 2 and the known charge pump circuit 10 in FIG. 1 are the signals connected to the gates of the transistors.

The gates of all the NMOST transistors of the charge pump circuit 20 of FIG. 2 are now connected to a next stage and the gates of all the PMOS transistors are connected to a previous stage. Also two extra capacitors, C₇ and C₈, and two extra NMOST transistors, T₁₃ and T₁₄, may be added on top of the circuit to generate the clock signals CLK_(p5) and CLK_(n5). These components can however be very small, since they do not directly pass the load current.

The gates of the NMOST switches of a voltage doubler circuit in one stage are driven by voltage doubler circuits in higher stages. The gates of the PMOS switches of a voltage doubler circuit in one stage are driven by voltage doubler circuits in lower stages.

The charge pump circuit of FIG. 2 may comprise any number of voltage doubler circuits.

The gates of any of the NMOST transistors of a double voltage circuit may be driven by a voltage doubler circuit in any higher stage. For instance, the first NMOST T₁ of the first double voltage circuit 21 of the charge pump circuit 20 of FIG. 2 may have its gate terminal G₁ connected to the first end c₆₁ of capacitor C₆ of the third double voltage circuit 23 instead to the first end c₄₁ of capacitor C₄ of the second double voltage circuit 22 of the charge pump circuit 20 of FIG. 2.

The gates of any of the PMOST transistors of a double voltage circuit may be driven by a voltage doubler circuit in any lower stage. For instance, the eleventh PMOST T₁₁ of the third double voltage circuit 23 of the charge pump circuit 20 of FIG. 2 may have its gate terminal G₁₁ connected to the first end c₂₁ of capacitor C₂ of the first double voltage circuit 21 instead to the first end c₄₁ of capacitor C₄ of the second double voltage circuit 22 of the charge pump circuit 20 of FIG. 2.

The gates of any of the PMOST transistors and/or the gates of any of the NMOST transistors of a double voltage circuit may be driven by a double voltage circuit of the same stage. I.e., some of the gates of the PMOST transistors of a double voltage circuit may be driven by a voltage doubler circuit in a lower stage and some of the gates of the PMOST transistors of a double voltage circuit may be driven by the voltage doubler circuit to which they belong. For instance, the eleventh PMOST T₁₁ of the third double voltage circuit 23 of the charge pump circuit 20 of FIG. 2 may have its gate terminal G₁₁ connected to the first end c₆₁ of capacitor C₆ of the third double voltage circuit 23 of the charge pump circuit 20 of FIG. 2.

Any combination of the above described may be possible.

FIG. 3 illustrates the pump charge circuit of FIG. 2 including start up transistors.

The pump charge circuit 30 of FIG. 3 comprises all the elements of FIG. 2 connected in the same way.

The first double circuit 31 of the pump charge circuit 30 of FIG. 3 includes the same elements of the first double circuit 21 of the pump charge circuit 20 of FIG. 2 and also includes a fifteenth NMOST T₁₅ and a sixteenth NMOST T_(16.) The source S₁₅ of the fifteenth NMOST T₁₅ and the source S₁₆ of the sixteenth NMOST T₁₆ are connected to the input V_(in1) of the first double voltage circuit 31 of the charge pump circuit 30 of FIG. 3.

The drain D₁₅ of the fifteenth NMOST T₁₅ is connected to the second end c₁₂ of capacitor C₁, to the drain D₁ of the first NMOST T₁ and to the drain D₃ of the third PMOST T₃.

The drain D₁₆ of the sixteenth NMOST T₁₆ is connected to the first end c₂₁ of capacitor C₂, to the drain D₂ of the second NMOST T₂ and to the drain D₄ of the fourth PMOST T₄.

The gate G₁₅ of the fifteenth NMOST T₁₅ is connected to the first end c₂₁ of capacitor C₂.

The gate G₁₆ of the sixteenth NMOST T₁₆ is connected to the second end c₁₂ of capacitor C₁.

The second double circuit 32 of the pump charge circuit 30 of FIG. 3 includes the same elements of the second double circuit 22 of the pump charge circuit 20 of FIG. 2 and also includes a seventeenth NMOST T₁₇ and an eighteenth NMOST T₁₈. The source S₁₇ of the seventeenth NMOST T₁₇ and the source S₁₈ of the eighteenth NMOST T₁₈ are connected to the input V_(in2) of the second double voltage circuit 32 of the charge pump circuit 30 of FIG. 3.

The drain D₁₇ of the seventeenth NMOST T₁₇ is connected to the second end c₃₂ of capacitor C₃, to the drain D₅ of the fifth NMOST T₅ and to the drain D₇ of the seventh PMOST T₇.

The drain D₁₈ of the eighteenth NMOST T₁₈ is connected to the first end c₄₁ of capacitor C₄, to the drain D₆ of the sixth NMOST T₆ and to the drain D₈ of the eighth PMOST T₈.

The gate G₁₇ of the seventeenth NMOST T₁₇ is connected to the first end c₄₁ of capacitor C₄.

The gate G₁₈ of the eighteenth NMOST T₁₈ is connected to the second end c₃₂ of capacitor C₃.

The third double circuit 33 of the pump charge circuit 30 of FIG. 3 includes the same elements of the third double circuit 23 of the pump charge circuit 20 of FIG. 2 and also includes a nineteenth NMOST T₁₉ and a twentieth NMOST T₂₀. The source S₁₉ of the nineteenth NMOST T₁₉ and the source S₂₀ of the twentieth NMOST T₂₀ are connected to the input V_(in3) of the third double voltage circuit 33 the charge pump circuit 30 of FIG. 3.

The drain D₁₉ of the nineteenth NMOST T₁₉ is connected to the second end c₅₂ of capacitor C₅, to the drain D₉ of the ninth NMOST T₉ and to the drain D₁₁ of the eleventh PMOST T₁₁.

The drain D₂₀ of the twentieth NMOST T₂₀ is connected to the first end c₆₁ of capacitor C₆, to the drain D₁₀ of the tenth NMOST T₁₀ and to the drain D₁₂ of the twelfth PMOST T₁₂.

The gate G₁₉ of the nineteenth NMOST T₁₉ is connected to the first end c₆₁ of capacitor C₆.

The gate G₂₀ of the twentieth NMOST T₂₀ is connected to the second end c₅₂ of capacitor C₅.

The transistors added in FIG. 3 compared to FIG. 2 are exactly the same NMOST transistors as in the known charge pump circuit of FIG. 1. They make sure that the capacitors are charged, even if the next-stage is not yet at its intended voltage and the block NMOST transistors are not turned-on properly. This prevents a potential dead-lock situation.

FIG. 4 illustrates an alternative voltage doubler circuit that may be used in the charge pump circuit of FIG. 2 or FIG. 3. The voltage doubler circuit of FIG. 4 comprises a NMOST T_(a) having a gate G_(a), a drain D_(a) and a source S_(a), a NMOST T_(b) having a gate G_(b), a drain D_(b) and a source S_(b), a PMOS T_(c) having a gate G_(c), a drain D_(c) and a source S_(c), a NMOST T_(d) having a gate G_(d), a drain D_(d) and a source S_(d), a capacitor C_(pN) having a first end c_(pN1) and a second end C_(pN2), a capacitor C_(nN) having a first end c_(nN1) and a second end c_(nN2), a first clock generator CLK_(p(1)) connected to first end c_(pN1), and a second clock generator CLK_(n(1)) connected to second end c_(nN2). The voltage doubler circuit of FIG. 4 comprises the same elements as any of the voltage doubler elements of the charge pump circuit of FIG. 2. The only difference is that the bulk terminals of the transistors are connected to its gate. The transistors can be turned-on a little harder by also driving the bulk from the clock-signals that drive the gate. The drawback is an increase in area, but this will be compensated by the transistors that can become smaller for a similar on-resistance.

FIG. 5 illustrates a charge pump circuit according to another embodiment of the invention.

The charge-pump circuit 50 of FIG. 5, seen from down to up, comprises a series circuit of first voltage doubler circuit 51, a second voltage doubler circuit 52, and a third voltage doubler circuit 53. The charge-pump circuit 50 of FIG. 5 may comprise any number of first voltage doubler circuits.

The charge pump circuit 50 of FIG. 5 comprises a plurality of transistors T_(i) (i=1, 2 . . . 12, 21 . . . 30). Each one of these transistors T_(i) has a respective gate G_(i), a source S_(i), and a drain D_(i). For the sake of simplicity, a transistor T_(i) will be called an i^(th) transistor in the specification hereinafter. The charge pump circuit 50 of FIG. 5 also comprises a plurality of capacitors C_(j) (j=1, 2 . . . 16). Each one of these capacitors C_(j) has a first end c_(j1) and a second end c_(j2). It is observed that the reference number concerned may be different in the claims, as they may appear in another order in the claims.

FIG. 5, also shows the voltage received and delivered by each of the voltage doubler circuits: the first voltage doubler circuit 51 is arranged to receive a voltage V_(in1) from the input V_(in) of the charge pump circuit and to deliver a voltage V_(out1) to the second voltage doubler circuit 52, the second voltage doubler circuit 52 is arranged to receive a voltage V_(in2) and to deliver a voltage V_(out2) to the third voltage doubler circuit 53, and the third voltage doubler circuit 53 is arranged to receive a voltage V_(in3) and to deliver a voltage V_(out3) to the output V_(out) of the charge pump circuit 50 of FIG. 5.

The charge pump circuit 50 of FIG. 5 comprises a first clock signal generator CLK_(p) and a second clock signal generator CLK_(n). The first clock signal generator CLK_(p) is configured to generate a first clock signal and the a second clock signal generator CLK_(n) is configured to generate a second clock signal, wherein the second clock signal is low when the first clock signal is high and the second clock signal is high when the first clock signal is low.

The charge pump circuit 50 of FIG. 5 may comprise a capacitor C_(out) having a first end c_(out1) and a second end c_(out2). The first end c_(out1) of C_(out) may be connected to the output V_(out) of the charge pump circuit 50 of FIG. 5. The second end c_(out2) of C_(out) may be connected to the ground.

The first voltage doubler circuit 51 of the charge pump circuit 50 of FIG. 5 includes a first NMOST T₁, a second NMOST T₂, a third PMOST T₃, a fourth PMOST T₄, a twenty-first PMOST T₂₁ and a twenty-second PMOST T₂₂. The first voltage doubler circuit 51 of the charge pump circuit 50 of FIG. 5 also includes a first capacitor C₁ having a first end c₁₁ and a second end c₁₂, a second capacitor C₂ having a first end c₂₁ and a second end c₂₂, ninth capacitor C₉ having a first end c₉₁ and a second end c₉₂, and a tenth capacitor C₁₀ having a first end c₁₀₁ and a second end c₁₀₂. The first NMOST T₁ and the second NMOST T₂ have their source terminals S₁ and S₂ connected to the input V_(in) of the charge pump circuit 50 of FIG. 5 and their drain terminals D₁ and D₂ connected respectively to the second end c₁₂ of capacitor C₁ and to the first end c₂₁ of capacitor C₂. The drain terminal D₁ of the first NMOST T₁ is also connected to the drain terminal D₃ of the third PMOST T₃, to the source terminal S₂₁ of the twenty-first PMOST T₂₁, and to the gate terminal G₂₂ of the twenty-second PMOST T₂₂. The drain terminal D₂ of the second NMOST T₂ is also connected to the drain terminal D₄ of the fourth PMOST T₄, to the source terminal S₂₂ of the twenty-second PMOST T₂₂, and to the gate terminal G₂₁ of the twenty-first PMOST T₂₁. The third PMOST T₃ and the fourth PMOST T₄ have their source terminals S₃ and S₄ connected to the voltage output V_(out1) of the first double voltage circuit 51.

The first NMOST T₁ has its gate terminal G₁ connected to the drain terminal D₂₁ of the twenty-first PMOST T₂₁ and to the first end c₁₀₁ of the capacitor C₁₀.

The second NMOST T₂ has its gate terminal G₂ connected to the drain terminal D₂₂ of the twenty-second PMOST T₂₂ and to the second end c₉₂ of the capacitor C₉.

The third PMOST T₃ has its gate terminal G₃ connected to the second clock signal generator CLK_(n).

The fourth PMOST T₄ has its gate terminal G₄ connected to the first clock signal generator CLK_(p).

The voltage output V_(out1) of the first double voltage circuit 51 of the charge pump circuit 50 of FIG. 5 is connected to the voltage input V_(in2) of the second voltage doubler circuit 52 of the charge pump circuit 50.

The second voltage doubler circuit 52 of the charge pump circuit 50 of FIG. 5 includes a fifth NMOST T₅, a sixth NMOST T₆, a seventh PMOST T₇, an eighth PMOST T₈, a twenty-third PMOST T₂₃, a twenty-fourth PMOST T₂₄, a twenty-fifth NMOST T₂₅ and a twenty-sixth NMOST T₂₆. The second voltage doubler circuit 52 of the charge pump circuit 50 of FIG. 5 also includes a third capacitor C₃ having a first end c₃₁ and a second end c₃₂, a fourth capacitor C₄ having a first end c₄₁ and a second end c₄₂, an eleventh capacitor C₁₁ having a first end c₁₁₁ and a second end c₁₁₂, a twelfth capacitor C₁₂ having a first end c₁₂₁ and a second end c₁₂₂, a thirteenth capacitor C₁₃ having a first end c₁₃₁ and a second end c₁₃₂, and a fourteenth capacitor C₁₄ having a first end c₁₄₁ and a second end c₁₄₂. The fifth NMOST T₅ and the sixth NMOST T₆ have their source terminals S₅ and S₆ connected to the input V_(in2) of the second voltage doubler circuit 52 of the charge pump circuit 50 of FIG. 5, and their drain terminals D₅ and D₆ connected respectively to the second end c₃₂ of capacitor C₃ and to the first end c₄₁ of capacitor C₄.

The drain terminal D₅ of the fifth NMOST T₅ is also connected to the drain terminal D₇ of the seventh PMOST T₇, to the source terminal S₂₃ of the twenty-third PMOST T₂₃, to the source terminal S₂₅ of the twenty-fifth NMOST T₂₅, to the gate terminal G₂₄ of the twenty-fourth PMOST T₂₄, and to the gate terminal G₂₆ of the twenty-sixth NMOST T₂₆.

The drain terminal D₆ of the sixth NMOST T₆ is also connected to the drain terminal D₈ of the eighth PMOST T₈, to the source terminal S₂₄ of the twenty-fourth PMOST T₂₄, to the source terminal S₂₆ of the twenty-sixth NMOST T₂₆, to the gate terminal G₂₃ of the twenty-third PMOST T₂₃, and to the gate terminal G₂₅ of the twenty-fifth NMOST T₂₅.

The fifth NMOST T₅ has its gate terminal G₅ connected to the drain terminal D₂₃ of the twenty-third PMOST T₂₃ and to the first end c₁₂₁ of the capacitor C₁₂.

The sixth NMOST T₆ has its gate terminal G₆ connected to the drain terminal D₂₄ of the twenty-fourth PMOST T₂₄ and to the second end c₁₁₂ of the capacitor C₁₁.

The seventh PMOST T₇ has its gate terminal G₇ connected to the drain terminal D₂₅ of the twenty-fifth NMOST T₂₅ and to the first end c₁₄₁ of the capacitor C₁₄.

The eighth PMOST T₈ has its gate terminal G₈ connected to the drain terminal D₂₆ of the twenty-sixth NMOST T₂₆ and to the second end c₁₃₂ of the capacitor C₁₃.

The seventh PMOST T₇ and the eighth PMOST T₈ have their source terminals S₇ and S₈ connected to the output V_(out2) of the second double voltage circuit 52.

The output V_(out2) of the second double voltage circuit 52 of the charge pump circuit 50 of FIG. 5 is connected to the input V_(in3) of the third voltage doubler circuit 53 of the charge pump circuit 50.

The third voltage doubler circuit 53 of the charge pump circuit 50 of FIG. 5 includes a ninth NMOST T₉, a tenth NMOST T₁₀, a eleventh PMOST T₁₁, a twelfth PMOST T₁₂, a twenty-seventh PMOST T₂₇, a twenty-eighth PMOST T₂₈, a twenty-ninth NMOST T₂₉ and a thirtieth NMOST T₃₀. The third voltage doubler circuit 53 of the charge pump circuit 50 of FIG. 5 also includes a fifth capacitor C₅ having a first end c₅₁ and a second end c₅₂, a sixth capacitor C₆ having a first end c₆₁ and a second end c₆₂, a fifteenth capacitor C₁₅ having a first end c₁₅₁ and a second end c₁₅₂, a sixteenth capacitor C₁₆ having a first end c₁₆₁ and a second end c₁₆₂, a seventeenth capacitor C₁₇ having a first end c₁₇₁ and a second end c₁₇₂, and a eighteenth capacitor C₁₈ having a first end c₁₈₁ and a second end c₁₈₂.

The ninth NMOST T₉ and the tenth NMOST T₁₀ have their source terminals S₉ and S₁₀ connected to the input V_(in3) of the third voltage doubler circuit 53 of the charge pump circuit 50 of FIG. 5, and their drain terminals D₉ and D₁₀ connected respectively to the second end c₅₂ of capacitor C₅ and to the first end c₆₁ of capacitor C₆.

The drain terminal D₉ of the ninth NMOST T₉ is also connected to the drain terminal D₁₁ of the eleventh PMOST T₁₁, to the source terminal S₂₇ of the twenty-seventh PMOST T₂₇, to the source terminal S₂₉ of the twenty-ninth NMOST T₂₉, to the gate terminal G₂₈ of the twenty-eighth PMOST T₂₈, and to the gate terminal G₃₀ of the thirtieth NMOST T₃₀.

The drain terminal D₁₀ of the tenth NMOST T₁₀ is also connected to the drain terminal D₁₂ of the twelfth PMOST T₁₂, to the source terminal S₂₈ of the twenty-eighth PMOST T₂₈, to the source terminal S₃₀ of the thirtieth NMOST T₃₀, to the gate terminal G₂₇ of the twenty-seventh PMOST T₂₇, and to the gate terminal G₂₉ of the twenty-ninth NMOST T₂₉.

The ninth NMOST T₉ has its gate terminal G₉ connected to the drain terminal D₂₇ of the twenty-seventh PMOST T₂₇ and to the first end c₁₆₁ of the capacitor C₁₆.

The tenth NMOST T₁₀ has its gate terminal G₁₀ connected to the drain terminal D₂₈ of the twenty-eighth PMOST T₂₈ and to the second end c₁₅₂ of the capacitor C₁₅.

The eleventh NMOST T₁₁ has its gate terminal G₁₁ connected to the drain terminal D₂₉ of the twenty-ninth NMOST T₂₉ and to the first end c₁₈₁ of the capacitor C₁₈.

The twelfth NMOST T₁₂ has its gate terminal G₁₂ connected to the drain terminal D₃₀ of the thirtieth NMOST T₃₀ and to the second end c₁₇₂ of the capacitor C₁₇.

The eleventh PMOST T₁₁ and the twelfth PMOST T₁₂ have their source terminals S₁₁ and S₁₂ connected to the output V_(out3) of the third double voltage circuit 53.

The output V_(out3) of the third double voltage circuit 53 of the charge pump circuit 50 of FIG. 5 may be connected to the output V_(out) of the charge pump circuit 50.

The first clock signal generator CLK_(p) of the charge pump circuit 50 of FIG. 5 is connected to the first end c₁₁ of capacitor C₁, to the first end c₃₁ of capacitor C₃, to the first end c₅₁ of capacitor C₅, to the first end c₉₁ of capacitor C₉, to the first end c₁₁₁ of capacitor C₁₁, to the first end c₁₃₁ of capacitor C₁₃, to the first end c₁₅₁ of capacitor C₁₅ and to the first end c₁₇₁ of capacitor C₁₇. The second clock signal generator CLK_(n) of the charge pump circuit 50 of FIG. 5 is connected to the second end c₂₂ of capacitor C₂, to the second end c₄₂ of capacitor C₄, to the second end c₆₂ of capacitor C₆, to the second end c₁₀₂ of capacitor C₁₀, to the second end c₁₂₂ of capacitor C₁₂, to the second end c₁₄₂ of capacitor C₁₄, to the second end c₁₆₂ of capacitor C₁₆ and to the second end c₁₈₂ of capacitor C₁₈.

The drawback of the charge pump circuit in FIG. 2 is that when the charge-pump circuit is not yet properly started (that means 2×V_(DD) is not yet 2×V_(DD) but close to V_(DD), and 3×V_(DD) is not yet 3×V_(DD) but also close to V_(DD), etc.), the signals driving the gates of the transistors are all toggling between V_(DD) and (2×V_(DD)). In this situation, the charge-pump circuit of FIG. 2 will behave similar to the known charge pump circuit of FIG. 1.

The same gate voltage driving the switches can be achieved by the charge pump circuit 50 of FIG. 5. The components are added compared to 2 can be small, so the cost is not large.

The big advantage is that the charge pump circuit of FIG. 5 will also improve over the charge pump circuit of FIG. 1, even when the charge-pump circuit is not started.

In the voltage doubler circuit 51, two capacitors and 2 transistors are missing compared to the rest of the voltage doubler circuits of FIG. 5. That is because the signals they were supposed to generate are equal to the input clock-signals, therefore the first clock generator CLK_(n1) and the second clock generator CLK_(p1) can be used directly.

The charge pump circuit of FIG. 5 may comprise any number of voltage doubler circuits.

The gates of any of the NMOST transistors of a double voltage circuit may be driven by a voltage doubler circuit in a higher stage as in FIG. 2

The gates of any of the PMOST transistors of a double voltage circuit may be driven by a voltage doubler circuit in a lower stage as in FIG. 2.

The gates of any of the PMOST transistors and/or the gates of any of the NMOST transistors of a double voltage circuit may be driven by a double voltage circuit of the same stage. I.e., some of the gates of the PMOST transistors of a double voltage circuit may be driven by a voltage doubler circuit in a lower stage and some of the gates of the PMOST transistors of a double voltage circuit may be driven by the voltage doubler circuit to which they belong.

Any combination of the voltage doubler circuits described in relation to FIG. 1-5 may be possible.

FIG. 6 illustrates the pump charge circuit of FIG. 5 including start up transistors.

The pump charge circuit 60 of FIG. 6 comprises all the elements of FIG. 5 connected in the same way.

The first double circuit 61 of the pump charge circuit 60 of FIG. 6 also includes a fifteenth NMOST T₁₅ and a sixteenth NMOST T₁₆. The source S₁₅ of the fifteenth NMOST T₁₅ and the source S₁₆ of the sixteenth NMOST T₁₆ are connected to the input V_(in1) of the first double voltage circuit 61 of the charge pump circuit 60 of FIG. 6.

The drain D₁₅ of the fifteenth NMOST T₁₅ is connected to the second end c₁₂ of capacitor C₁, to the drain D₁ of the first NMOST T₁ and to the drain D₃ of the third PMOST T₃.

The drain D₁₆ of the sixteenth NMOST T₁₆ is connected to the first end c₂₁ of capacitor C₂, to the drain D₂ of the second NMOST T₂ and to the drain D₄ of the fourth PMOST T₄.

The gate G₁₆ of the sixteenth NMOST T₁₆ is connected to the second end c₁₂ of capacitor C₁.

The gate G₁₅ of the fifteenth NMOST T₁₅ is connected to the first end c₂₁ of capacitor C₂.

The second double circuit 62 of the pump charge circuit 60 of FIG. 6 also includes a seventeenth NMOST T₁₇ and an eighteenth NMOST T₁₈. The source S₁₇ of the seventeenth NMOST T₁₇ and the source S₁₈ of the eighteenth NMOST T₁₈ are connected to the input V_(in2) of the second double voltage circuit 62 of the charge pump circuit 60 of FIG. 6.

The drain D₁₇ of the seventeenth NMOST T₁₇ is connected to the second end c₃₂ of capacitor C₃, to the drain D₅ of the fifth NMOST T₅ and to the drain D₇ of the seventh PMOST T₇.

The drain D₁₈ of the eighteenth NMOST T₁₈ is connected to the first end c₄₁ of capacitor C₄, to the drain D₆ of the sixth NMOST T₆ and to the drain D₈ of the eighth PMOST T₈.

The gate G₁₇ of the seventeenth NMOST T₁₇ is connected to the first end c₄₁ of capacitor C₄.

The gate G₁₈ of the eighteenth NMOST T₁₈ is connected to the second end c₃₂ of capacitor C₃.

The third double circuit 63 of the pump charge circuit 60 of FIG. 6 also includes a nineteenth NMOST T₁₉ and a twentieth NMOST T₂₀. The source S₁₉ of the nineteenth NMOST T₁₉ and the source S₂₀ of the twentieth NMOST T₂₀ are connected to the input V_(in3) of the third double voltage circuit 63 of the charge pump circuit 60 of FIG. 6.

The drain D₁₉ of the nineteenth NMOST T₁₉ is connected to the second end c₅₂ of capacitor C₅, to the drain D₉ of the ninth NMOST T₉ and to the drain D₁₁ of the eleventh PMOST T₁₁.

The drain D₂₀ of the twentieth NMOST T₂₀ is connected to the first end c₆₁ of capacitor C₆, to the drain D₁₀ of the tenth NMOST T₁₀ and to the drain D₁₂ of the twelfth PMOST T₁₂.

The gate G₁₉ of the nineteenth NMOST T₁₉ is connected to the first end c₆₁ of capacitor C₆.

The gate G₂₀ of the twentieth NMOST T₂₀ is connected to the second end c₅₂ of capacitor C₅.

Any combination of the voltage doubler circuits described in relation to FIG. 1-6 may be possible.

FIG. 7 shows simulation results comparing the charge pump circuit of FIG. 1 and the charge pump circuit of FIG. 2. The horizontal axe shows the output voltage V_(out) in millivolts. The vertical axe shows the load current in microampere. The bulk of each transistor is connected to its gate. The input voltage V_(in) is 0.15 volts.

As can be seen, the charge pump circuit of FIG. 2 can deliver significantly more current than the charge pump circuit of FIG. 1.

It will be clear to a person skilled in the art that the scope of the invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the invention as defined in the attached claims. While the invention has been illustrated and described in detail in the figures and the description, such illustration and description are to be considered illustrative or exemplary only, and not restrictive. The present invention is not limited to the disclosed embodiments but comprises any combination of the disclosed embodiments that can come to an advantage. The invention is limited by the attached claims and their technical equivalents only.

Variations to the disclosed embodiments can be understood and effected by a person skilled in the art in practicing the claimed invention, from a study of the figures, the description and the attached claims. In the description and claims, the word “comprising” does not exclude other elements, and the indefinite article “a” or “an” does not exclude a plurality. In fact it is to be construed as meaning “at least one”. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the invention. 

What is claimed is:
 1. A charge pump circuit comprising: a number n of voltage doubler circuits, with n>1; a first clock signal generator configured to generate a first clock signal; a second clock signal generator configured to generate a second clock signal, wherein the second clock signal is low when the first clock signal is high and the second clock signal is high when the first clock signal is low; wherein each one of the n voltage doubler circuits comprises: an input; an output; a first capacitor having a first and a second terminal, wherein the first terminal is connected to the first clock signal generator; a second capacitor having a first and a second terminal, wherein the first terminal is connected to the second clock signal generator; a first N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the first NMOST is connected to the input of the voltage doubler circuit and the drain of the first NMOST is connected to the second terminal of the first capacitor; a second N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the second NMOST is connected to the source of the first NMOST and the drain of the second NMOST is connected to the second terminal of the second capacitor; a first P-type metal oxide semiconductor transistor (PMOST) having a source, a drain and a gate, wherein the drain of the first PMOST is connected to the second terminal of the first capacitor and the source of the first PMOST is connected to the output of the voltage doubler circuit; a second P-type metal oxide semiconductor transistor (PMOST) having a source, a drain and a gate, wherein the source of the second PMOST is connected to the source of the first PMOST and the drain of the second PMOST is connected to the second terminal of the second capacitor; wherein the output of the i-th voltage doubler circuit is the input of the (i+1)-th voltage doubler circuit for every i from 1 to n−1; wherein at least a k-th voltage doubler circuit of the n voltage doubler circuits has: the gate of the first PMOST and/or the gate of the second PMOST connected respectively to the second terminal of the second capacitor and/or to the second terminal of the first capacitor of an m-th voltage doubler circuit, wherein m<k; and/or the gate of the first NMOST and/or the gate of the second NMOST connected respectively to the second terminal of the second capacitor and/or to the second terminal of the first capacitor of a j-th voltage doubler circuit, wherein j>k.
 2. A voltage doubler circuit comprising: an input; an output; a first capacitor having a first and a second terminal, wherein the first terminal is configured to receive a first clock signal; a second capacitor having a first and a second terminal, wherein the first terminal is configured to receive a second clock signal and wherein the second clock signal is low when the first clock signal is high and the second clock signal is high when the first clock signal is low; a first N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the first NMOST is connected the input of the voltage doubler circuit and the drain of the first NMOST is connected to the second terminal of the first capacitor; a second N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the second NMOST is connected to the source of the first NMOST and the drain of the second NMOST is connected to the second terminal of the second capacitor; a first P-type metal oxide semiconductor transistor (PMOST) having a source, a drain and a gate, wherein the drain of the first PMOST is connected to the second terminal of the first capacitor and the source of the first PMOST is connected to the output of the voltage doubler circuit; a second P-type metal oxide semiconductor (PMOST) having a source, a drain and a gate, wherein the source of the second PMOST is connected to the source of the first NMOST and the drain of the second NMOST is connected to the second terminal of the second capacitor; a third capacitor having a first terminal configured to receive the first clock signal and a second terminal connected to the gate of the second NMOST; a fourth capacitor having a first terminal configured to receive the second clock signal and a second terminal connected to the gate of the first NMOST; a third P-type metal oxide semiconductor transistor (PMOST) having a source, a drain and a gate, wherein the source of the third PMOST is connected to the second terminal of the first capacitor, the drain of the third PMOST is connected to the second terminal of the fourth capacitor, and the gate of the third PMOST is connected to the second terminal of the second capacitor; a fourth P-type metal oxide semiconductor transistor (PMOST) having a source, a drain and a gate, wherein the source of the fourth PMOST is connected to the second terminal of the second capacitor, the drain of the fourth PMOST is connected to the second terminal of the third capacitor, and the gate of the fourth PMOST is connected to the second terminal of the first capacitor; and/or a fifth capacitor having a first terminal configured to receive the first clock signal and a second terminal connected to the gate of the second PMOST, a sixth capacitor having a first terminal configured to receive the second clock signal and a second terminal connected to the gate of the first PMOST, a third N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the third NMOST is connected to the second terminal of the first capacitor, the drain of the third NMOST is connected to the second terminal of the sixth capacitor, and the gate of the third NMOST is connected to the second terminal of the second capacitor, a fourth N-type metal oxide semiconductor transistor (PMOST) having a source, a drain and a gate, wherein the source of the fourth NMOST is connected to the second terminal of the second capacitor, the drain of the fourth NMOST is connected to the second terminal of the fifth capacitor, and the gate of the fourth NMOST is connected to the second terminal of the first capacitor.
 3. A charge pump circuit comprising: a number n of voltage doubler circuits wherein at least one of the n voltage doubler circuits is the voltage doubler circuit of claim 1 and wherein n>1; a first clock signal generator configured to generate the first clock signal; a second clock signal generator configured to generate the second clock signal; wherein the output of the i-th voltage doubler circuit is connected to the input of the (i+1)-th voltage doubler circuit for 0<i<n−1;
 4. The charge pump circuit of claim 1, further comprising a (n+1)-th stage, wherein the (n+1)-th stage comprises: a first capacitor having a first and a second terminal, wherein the first terminal of the first capacitor is connected to the first clock signal generator; a second capacitor having a first and a second terminal, wherein the first terminal of the second capacitor is connected to the second clock signal generator; a first N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the first NMOST is connected to the output of the n-th voltage doubler, the drain of the first NMOST is connected to the second terminal of the first capacitor and the gate of the first NMOST is connected to the second terminal of the second capacitor; a second N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the second NMOST is connected to the output of the n-th voltage doubler, the drain of the second NMOST is connected to the second terminal of the second capacitor, and the gate of the second NMOST is connected to the second terminal of the first capacitor.
 5. The charge pump circuit according to claim 1, or the voltage doubler circuit according to claim 2, wherein at least the k-th voltage doubler circuit of the n voltage doubler circuits of the charge pump circuit according to claim 1 or the voltage doubler circuit according to claim 2 further comprises a first start-up N-type metal oxide semiconductor transistor (NMOS) having a source, a drain and a gate, wherein the source is connected to the source of the first NMOS, the drain is connected to the drain of the first NMOST, and the gate is connected to the drain of the second NMOST.
 6. The charge pump circuit according to claim 1, or the voltage doubler circuit according to claim 2, wherein at least the k-th voltage doubler circuit of the n voltage doubler circuits of the charge pump circuit according to claim 1 or the voltage doubler circuit according to claim 2 further comprises a second start-up N-type metal oxide semiconductor transistor (NMOS) having a source, a drain and a gate, wherein the source is connected to the source of the second NMOST, the drain is connected to the drain of the second NMOST, and the gate is connected to the drain of the first NMOST.
 7. The charge pump circuit according to claim 1, or the voltage doubler circuit according to claim 2, wherein at least one of the MOSTs has a bulk terminal connected to its gate.
 8. A method of operating the charge pump circuit comprising the steps of: providing a number n of voltage doubler circuits, with n>1; providing a first clock signal generator to generate a first clock signal; providing a second clock signal generator to generate a second clock signal, wherein the second clock signal is low when the first clock signal is high and the second clock signal is high when the first clock signal is low; wherein each one of the n voltage doubler circuits comprises: an input; an output; a first capacitor having a first and a second terminal, wherein the first terminal is connected to the first clock signal generator; a second capacitor having a first and a second terminal, wherein the first terminal is connected to the second clock signal generator; a first N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the first NMOST is connected to the input of the voltage doubler circuit and the drain of the first NMOST is connected to the second terminal of the first capacitor; a second N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the second NMOST is connected to the source of the first NMOST and the drain of the second NMOST is connected to the second terminal of the second capacitor; a first P-type metal oxide semiconductor transistor (PMOST) having a source, a drain and a gate, wherein the drain of the first PMOST is connected to the second terminal of the first capacitor and the source of the first PMOST is connected to the output of the voltage doubler circuit; a second P-type metal oxide semiconductor transistor (PMOST) having a source, a drain and a gate, wherein the source of the second PMOST is connected to the source of the first PMOST and the drain of the second PMOST is connected to the second terminal of the second capacitor; wherein the output of the i-th voltage doubler circuit is the input of the (i+1)-th voltage doubler circuit for every i from 1 to n−1; wherein at least a k-th voltage doubler circuit of the n voltage doubler circuits has: the gate of the first PMOST and/or the gate of the second PMOST connected respectively to the second terminal of the second capacitor and/or to the second terminal of the first capacitor of an m-th voltage doubler circuit, wherein m<k; and/or the gate of the first NMOST and/or the gate of the second NMOST connected respectively to the second terminal of the second capacitor and/or to the second terminal of the first capacitor of a j-th voltage doubler circuit, wherein j>k and providing an input voltage V_(in) to the input; wherein if the first clock signal is low then the first NMOST and the second PMOST are conducting, the second NMOST and the first PMOST are in cut-off, and the first and second capacitors are charging; wherein if the first clock signal is high then the first NMOST and the second PMOST are in cut-off, the second NMOST and the first PMOST are conducting, and the first and second capacitors are discharging; and wherein the output provides an output voltage V_(out) which is larger than the input voltage V_(in)
 9. The method of operating a charge pump circuit of claim 8, further comprising a (n+1)-th stage, wherein the (n+1)-th stage comprises: a first capacitor having a first and a second terminal, wherein the first terminal of the first capacitor is connected to the first clock signal generator; a second capacitor having a first and a second terminal, wherein the first terminal of the second capacitor is connected to the second clock signal generator; a first N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the first NMOST is connected to the output of the n-th voltage doubler, the drain of the first NMOST is connected to the second terminal of the first capacitor and the gate of the first NMOST is connected to the second terminal of the second capacitor; a second N-type metal oxide semiconductor transistor (NMOST) having a source, a drain and a gate, wherein the source of the second NMOST is connected to the output of the n-th voltage doubler, the drain of the second NMOST is connected to the second terminal of the second capacitor, and the gate of the second NMOST is connected to the second terminal of the first capacitor.
 10. The method of operating a charge pump circuit according to claim 8, wherein at least the k-th voltage doubler circuit of the n voltage doubler circuits of the charge pump circuit according to claim 1 or the voltage doubler circuit according to claim 2 further comprises a first start-up N-type metal oxide semiconductor transistor (NMOS) having a source, a drain and a gate, wherein the source is connected to the source of the first NMOS, the drain is connected to the drain of the first NMOST, and the gate is connected to the drain of the second NMOST.
 11. The method of operating a charge pump circuit according to claim 8, wherein at least the k-th voltage doubler circuit of the n voltage doubler circuits of the charge pump circuit according to claim 1 or the voltage doubler circuit according to claim 2 further comprises a second start-up N-type metal oxide semiconductor transistor (NMOS) having a source, a drain and a gate, wherein the source is connected to the source of the second NMOST, the drain is connected to the drain of the second NMOST, and the gate is connected to the drain of the first NMOST.
 12. The method of operating a charge pump circuit according to claim 8, wherein at least one of the MOSTs has a bulk terminal connected to its gate. 